Muscone is a macrocyclic ketone well appreciated in the perfumery industry owing to its musky odor. A variety of processes for the preparation of muscone have been disclosed to this day. However, these prior art methods are not easily applied to large scale production, either because of their complexity, or owing to the low yields obtained in certain steps which are critical for the overall synthesis. One of the known processes makes use of the compounds of formula ##STR5## [see DE-OS 29 16 413, published on 6.11.1980], which compounds are subjected to hydrogenation, respectively acidic isomerisation, to give a compound of formula ##STR6## which, by ozonolysis followed by reduction, provides the desired muscone.
The starting products in the above-cited process were obtained by a multi-step synthesis illustrated in the following diagram: ##STR7##
Another prior art process for the preparation of muscone resorts to the use of the compound of formula ##STR8## [see European patent No. 37116]. This compound was prepared by a process which comprises the addition of methallyl chloride to cyclododecanone, in alkaline medium, followed by the addition of thiophenol to the product thus obtained, oxidation by means of an organic peroxide and treatment of the resulting sulfone with a strong base.
The present invention provides a new process for the preparation of polyunsaturated cyclic compounds of formula ##STR9## having two conjugated double bonds in the endo- and exo- positions of the pentagonal cycle indicated by the dotted lines, and wherein symbols R.sup.1 and R.sup.2, when taken separately, represent respectively a. a linear or branched C.sub.1 to C.sub.4 alkyl radical and b. an hydrogen atom or a methyl radical, or, when taken together with the carbon atoms to which they are bonded form a polymethylenic cycle such as indicated by the dotted line, containing from 5 to 12 carbon atoms, and symbol R.sup.3 stands for an hydrogen atom or a methyl radical, n being an integer equal to 0 or 1.